1. Field of the Invention
Example embodiments of the present patent application relate to an image forming apparatus such as a copier, facsimile machine, printer, plotter, and multiple function machine including two or more functions of these apparatuses and devices that form images on both sides of a recording medium.
2. Discussion of the Related Art
Electrophotographic image forming apparatuses generally include a fixing unit that employs a heat fixing system for fixing a toner image formed on a recording medium to the recording medium by application of heat and pressure. During a fixing process performed by the heat fixing system, moisture contained in the recording medium evaporates therefrom, which builds up condensation in the electrophotographic image forming apparatus.
Several techniques have been proposed to reduce or eliminate the accumulation of condensation in the image forming apparatus.
For example, in some related-art image forming apparatuses, if a fixing unit, which fixes an image to a transfer sheet serving as a recording medium by application of heat and pressure, starts to fix the image when the temperature in the related-art image forming apparatus is relatively low, moisture in the transfer sheet evaporates and builds up as condensation on transfer sheet guide plates that form sheet conveyance paths of the image forming apparatus.
Such a sheet conveyance path is generally provided to an image forming apparatus for a transfer sheet to pass therethrough when printing an image on a single side or both sides of the transfer sheet. The sheet conveyance path has a relatively small amount of water because the transfer sheet is heated in the fixing unit and therefore a temperature of the transfer sheet guide plate is increased, and the transfer sheet passing through the sheet transfer conveyance path draws moisture from the image forming apparatus.
Further, some related-art image forming apparatuses include an outer cover that has a guide member for forming the fixing unit and a transfer sheet reverse path, and a hollow portion that is formed between the guide member and the outer cover in order to further reduce the creation of water droplets and prevent condensation in the image forming apparatus.
However, these approaches require additional components and add to the overall size of the apparatus, which is undesirable in the face of continued market demand for compact and inexpensive configurations.
Further, as the number of operations for allowing passage of transfer sheets such as single-side printing is increased, the transfer sheet reverse path formed of guide members can receive more water droplets adhered thereto. When printing both sides of a transfer sheet after completion of a large amount of single-side printing, water droplets accumulated on the transfer sheet reverse path can adhere to the transfer sheet. This action can cause transfer failure at a transfer part such as a secondary transfer roller while forming an image, and produce defective images as a result.
Specifically, a compact image forming apparatus having a sheet conveyance path extending in a vertical direction generally includes a transfer sheet reverse path with a branched section for printing both sides of a transfer sheet after fixing the first side thereof. This configuration can build up condensation more easily.
Condensation is most likely to accumulate immediately after fixing. To eliminate water droplets or liquid droplets, holes or slots are formed on a transfer surface of each guide to reduce an area to which water droplets adhere. However, water droplets can still adhere to the transfer sheet guide plates of the sheet reverse path while printing the first side of a transfer sheet. Similarly, a duct member or other element or component to reduce or eliminate water droplets or condensation cannot be provided to prevent adhesion of water droplets to the transfer sheet guide plates because space for such an additional component is limited and cost can increase due to an increasing number of mechanical parts.
In other related-art image forming apparatuses having a hollow portion provided for eliminating condensation, the configuration can be simple and low-cost because no additional unit or device to avoid water droplets is provided thereto. However, when a hollow portion is located above the transfer sheet reverse path, water vapor produced in the fixing unit can travel via the transfer sheet reverse path to the hollow portion, and therefore water vapor can build up and condense on the transfer sheet guide plates that form the transfer sheet reverse path before it reaches the hollow portion to accumulate as water droplets for condensation. The accumulated water droplets can adhere to the transfer sheet to cause transfer failure at the transfer section when printing both sides of a next transfer sheet, which can produce defective images.